Some big banks' rewards programs (ahem, Bank of America WorldPoints and Citi ThankYou) have stingy cash back rates, so redeeming your points for gift cards is your best option. If you really want to juice your return, sell those gift cards.

The credit card gurus at NerdWallet say you can get a 50% better cash back return by selling the gift cards you get from Citi's ThankYou program at a site like previously mentionedCardpool, which buys and sells gift cards. It's a similar situation for BoA WorldPoints. Here's why:

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[With BoA], rather than using 5,000 points to get $25, you can use 6,500 WorldPoints to get a $50 Whole Foods gift card. And if you're not in the habit of spending $5 apiece for locally-sourced organic grapes, you can sell that gift card on Cardpool right now* for $45.50. That translates to 0.7 cents, rather than 0.5 cents.

If you have Citi ThankYou points, Cardpool has even more to offer. To claim $50 in cash, you need 8,000 points, giving you a pretty sad exchange of $0.006 per point. And unlike BofA, no amount of points will ever get you 1 cent per point. Thankfully, they give you a full 1 cent back when you redeem for many gift cards, so you can grab a $50 Wal-Mart gift card for 5,000 points and sell it on Cardpool for $45. That's 0.9 cents per point-a full 50% better than Citi's own cash back rate!

The caveat is that Cardpool's prices change occasionally, so you'll need to double-check the amount you can get from selling a gift card. But NerdWallet says that you can almost mimic the cash rates of a decent cash back credit card (see some of the most popular ones here) using Cardpool.